1. Field of the Invention
The present invention relates to an arrangement of oil passages for supplying oil to a valve system in an internal combustion engine of a type having a valve system in a cylinder head.
2. Description of the Background Art
The internal combustion engine of this type requires an oil passage communicating a crank case side oil supply passage to a valve system disposed in a cylinder head over a crank case beyond a cylinder. The passage supplies lubrication oil not only to a specified bearing portion of a crank shaft and a transmission in the crank case, but also to the valve system.
The internal combustion engine having the above-described oil passage has been known, for example, as disclosed in Japanese Patent Publication No. SHO 59-24281. Hereinafter, one example of a conventional internal combustion engine of a four-cycle type for a motor-bicycle will be described with reference to FIGS. 4 and 5.
An internal combustion engine 01 is an overhead cam OHC engine, which includes a cylinder head 04 and a cam shaft 07 in a head cover 05. The cam shaft 07 positioned over a cylinder of a cylinder block 03 is separated from a crank shaft 06 in a crank case 02. Therefore, when driving the cam shaft 07, a cam chain 08 is hung between both the shafts.
Oil fed by an oil pump 09 assembled in the crank case 02 is supplied to a connecting rod 012 and bearing portions such as gears through oil passages in the crank shaft 06, a main shaft 010 of the transmission, and a counter shaft 011. Further, an oil pipe 015 connected to the oil passage provided in the crank case 02 extends exteriorly and is led upwardly along the outer surfaces of the cylinder block 03 and the cylinder head 04, and is in communication with the cylinder head 04 and an oil chamber 016 in the head cover 05.
The oil chamber 016 is disposed at the end portion of the cam shaft 07 for supplying oil in an oil passage 07a formed in the cam shaft 07. The oil passage 07a has a plurality of branched passages 07b toward the outer peripheral surface for supplying oil to bearing portions and the sliding contact surface of a rocker arm 017.
As described above, oil is supplied from the crank case 02 into the cylinder head 04 by way of the oil pipe 015 disposed outside the internal combustion engine 01. Since the oil pipe 015 is disposed outside the internal combustion engine, it is possible to avoid heat sources such as a cylinder and combustion chamber and expect a cooling effect. Therefore, oil can be supplied to the valve system without heating thereof.